“Thoracic aortic aneurysm” is the term used to describe a condition where a segment of the aorta in the thoracic region is dilated and is treatable when it reaches more than 50% of its original diameter. Thoracic aortic aneurysms are known to be caused by hardening of the arteries (atherosclerosis), high blood pressure (hypertension), congenital disorders such as Marfan's Syndrome, trauma, or less commonly, syphilis. Atherosclerosis is by far the most common cause. Thoracic aneurysms occur in the ascending aorta (approximately 25% of the time), the aortic arch (approximately 25% of the time) or the descending thoracic aorta (approximately 50% of the time).
The thoracic aorta has numerous arterial branches. The arch of the aorta has three major branches extending therefrom, all of which arise from the convex upper surface of the arch and ascend through the superior thoracic aperture to the root of the neck. The brachiocephalic artery originates anterior to the trachea. The brachiocephalic artery divides into two branches, the right subclavian artery (which supplies blood to the right arm) and the right common carotid artery (which supplies blood to the right side of the head and neck). The left common carotid artery arises from the arch of the aorta just to the left of the origin of the brachiocephalic artery. The left common carotid artery supplies blood to the left side of the head and neck. The third branch arising from the aortic arch, the left subclavian artery, originates behind and just to the left of the origin of the left common carotid artery and supplies blood to the left arm.
When an aneurysm of the aorta occurs, most patients have no symptoms until the aneurysm begins to leak or expand. Most non-leaking thoracic aneurysms of the aortic arch are detected by tests—usually a chest x-ray or a chest CT scan—that are run for other reasons. Chest or back pain may indicate acute expansion or leakage of the aneurysm. An aortogram (a special set of x-ray images made as a result of injection of dye into the aorta) also may identify the location and extent of the aneurysm and identify any branch arteries of the aorta that are also involved. For patients with thoracic aneurysms of the aortic arch, surgery to replace the aorta may be performed where the aorta is replaced with a fabric substitute in an operation that uses a heart-lung machine. In such a case, the aneurysmal portion of the aorta is removed or opened and a substitute lumen is sewn across the aneurysmal portion. Such surgery is highly invasive, requires an extended recovery period and, therefore, cannot be performed on individuals in fragile health or with other contraindicative factors.
Alternatively, the aneurysmal region of the aorta can be bypassed by use of a tubular exclusion device, e.g., by a stent graft placed inside the vessel spanning the aneurysmal portion of the vessel, to seal off the aneurysmal portion from further exposure to blood flowing through the aorta. A stent graft can be implanted without a chest incision, using specialized catheters that are introduced through arteries, usually through incisions in the groin region of the patient. The use of stent grafts to internally bypass, within the aorta or flow lumen, the aneurysmal site, is also not without issues. In particular, where a stent graft is used in a thoracic location, care must be taken so that critical branch arteries are not covered or occluded by the stent graft yet the stent graft must seal against the aorta wall and provide a flow conduit for blood to flow past the aneurysmal site. Where the aneurysm is located immediately adjacent to the branch arteries, there is a need to deploy the stent graft in a location which partially or fully extends across the location of the origin of the branch arteries from the aorta to ensure sealing of the stent graft to the artery wall. However, there is not presently an acceptable paradigm for enabling flow to the branch artery when a stent graft is deployed.
Additionally, where an aneurysm develops, an aortic dissection may develop as a side effect of the thinning of the aorta wall during an aneurysmal event or as a consequence of the weakening of the aorta wall which brought on the aneurysmal event. When such dissection occurs, an inner lumen wall layer and an outer lumen wall layer of the aorta become separated, such that a gap may form therebetween. If blood can access this gap, such as through a tear in the inner wall of the aorta, the dissection may increase in size and the inner blood vessel wall layer may extend inwardly of the flow lumen, reducing the flow cross-section for blood flow therethrough and forming a region between the inner and outer lumen wall layers where blood can collect under systemic pressure. This blood may further aggravate the aneurysmal condition, increasing the risk of a rupture of the aneurysm. Such a dissection may occur adjacent to, and extend from, the aneurysmal aortic site, such that the placement of a stent graft to exclude the aneurysm may not address the dissected lumen condition and fresh blood can access the dissection and perhaps, through the region between the lumen walls, supply fresh blood to the aneurysm leading to further progression thereof.
Thus, there is a desire in the art to achieve a greater success of aneurysm repair and healing of the aortic arch, and to address the dissected lumen wall condition.